This invention relates to wireless communication networks.
In recent years, the demand for wireless voice and data services has increased dramatically. In order to keep up with these demands, wireless network providers have focused on methods to increase the capacity of their existing wireless networks while minimizing the energy consumed by small portable devices. Wireless networks, ranging from fixed infrastructure wireless networks such as most of the currently deployed cellular networks to independent, dynamic multi-hop networks, are using various types of power control technology to meet these needs.
A typical fixed infrastructure wireless network 100 is shown in FIG. 1. It is divided into a plurality of cells 124. Each cell contains a fixed base station 126. Each base station 126 is connected to a centralized switch 128 that provides switching capabilities and acts as a gateway to wired networks such as the public switched telephone network (PSTN), the Internet, and other public and private data communications networks. On the customer side, users connect to the wireless network through wireless mobile nodes 122 that can act as transmitters and receivers. The mobile nodes 122 communicate with the base stations 126 over wireless communications links 108.
Dynamic, multi-hop networks consist of a plurality of mobile nodes that can act as transmitters, receivers and message routers and relays. This additional routing capability allows multi-hop routing through intermediate nodes in addition to single hop routing from a source node to a destination node. For example, if propagation characteristics change significantly between a source and destination node, the lowest energy path may be through other intermediate nodes instead of a direct route between the two nodes. Because these networks do not contain fixed base stations, the individual mobile nodes communicate with each other over wireless communications links. This network structure allows the mobile nodes to move freely, generating rapidly changing network topologies.
Dynamic, multi-hop networks may also contain a plurality of mobile hub nodes. These mobile hubs act as traffic concentrators similar to base stations in a typical fixed mobile network except these hubs are capable of limited mobility. Dynamic, multi-hop networks containing mobile hubs can be considered hybrid networks because they combine characteristics of dynamic networks and fixed infrastructure networks.
In nearly all types of wireless networks, power requirements and optimal transmission parameters for communication over wireless links can vary greatly even over distances of 100 feet or less because of natural and cultural features such as hills, trees, and buildings. For example, a mobile node may need to increase transmitted power to maintain reliable communications when traveling behind a building or through a heavily forested area. The mobile node may also benefit from adapting its transmission parameters (e.g., modulation, demodulation, and error control coding) to changing channel characteristics. The use of significantly inappropriate transmission parameters would likely require a further increase in transmitted power to maintain reliable communications. In addition, a mobile node may need to increase power and further adapt its transmission parameters to ensure reliable communication of data as its transmitted data rate increases.
When a mobile node increases power, interference with other mobile nodes may also be increased. The channel capacity of a wireless network is greatly influenced by this co-channel interference. An increase in interference between users can lower the ability of a wireless provider to reuse frequencies, resulting in a reduction of system capacity. Because of the tremendous demand for wireless voice and data services and increased competition between service providers, wireless network providers cannot afford such a reduction in system capacity. Therefore, wireless providers are continually striving to maximize system capacity, which in turn, requires limiting co-channel interference.
Prior techniques addressing efficient power control and transmission parameter adaptation in wireless networks use knowledge gained from past network and link measurements. For example, fixed infrastructure Code Division Multiple Access (CDMA) networks can use both open-loop and closed loop methods to provide power control. In open-loop power control, a transmitting mobile node estimates a transmission power based on measurements of the power level of signals received from the base station. In closed-loop power control, a receiving node (e.g., a base station) measures power level received from a transmitting node (e.g., mobile node). The receiving node determines whether the measured power is within a pre-defined power level. Based on these measurements taken by the receiving node, the receiving node periodically communicates power control commands to the transmitting node (e.g., decrease power, increase power).
For optimal power control and transmission parameter adaptation, these prior techniques require a mobile node to be in continuous or nearly continuous two-way communication with other nodes to obtain measurement of the characteristics of all potential paths. When two mobile nodes are in continuous communication, they can exchange information on received signal power and signal quality and each mobile node can adjust its transmitter power and adapt its transmission parameters to expend the minimum energy needed to maintain communication as the propagation environment between them changes. If the characteristics of the propagation paths between mobile nodes are known through continuous use of the paths, rerouting decisions in a multihop network can also be made optimally to minimize overall energy.
If, however, use of a particular link is sporadic, measurements of that path can become outdated and power control, transmission parameter adaptation, and routing would then be based on out-of-date information. If the new transmission is begun at too low a transmitted power or with inappropriate transmission parameters, it will not succeed and must be repeated at a higher power. If it is begun at too high a transmitted power, it will succeed but will expend excess energy. If the choice of a new route does not adequately reflect the actual path loss, additional energy may be expended transmitting information over inferior routes.
An objective of our invention is to provide a system and method that will proactively predict optimal communications characteristics (e.g., power level, transmission parameters, communication time and location) without relying on prior network measurements. It is yet another objective of our invention to provide a system and method with future advanced reservation capabilities that will allow the scheduling of future transmission at the optimal communication time and place.
It is a further objective of our invention to provide a system and method that will provide efficient power control and transmission parameter adaptation at a mobile node, thus reducing the drain on the mobile node""s battery power and decreasing the energy radiating from a mobile node""s antenna to accomplish a desired communication.
Our invention is directed to energy efficient power control, transmission parameter adaptation, routing, and scheduling in a wireless network. Our invention provides a wireless system that proactively predicts optimal characteristics such as power level, transmission parameters, transmission location, and time for communication between two nodes. The wireless system includes adaptive predictive mobile nodes and an autonomous or distributed network controller. In addition, the wireless system may also include traditional nodes such as handsets, mobile computers, and fixed base stations. The adaptive predictive mobile nodes include a position location technology element, a database, and a prediction processor. The prediction processor includes capabilities to predict the advantaged location, power level, transmission parameters, communication time, and route for communications between nodes.
In the first mode of operation of our invention, the wireless network uses the adaptive predictive capabilities of mobile nodes and the supporting capabilities distributed throughout other network nodes to provide energy efficient power control, transmission parameter adaptation, and routing for communications between nodes. In this mode, the adaptive predictive mobile node determines its current and predicted future position, the current and future predicted positions of other nodes in the network, and the priority of the data to be communicated. The adaptive predictive mobile node then executes the propagation prediction and power level prediction capabilities in the prediction processor. After executing these capabilities, the adaptive predictive node identifies an advantaged position, power level, and set of transmission parameters for communication with another node. This communication could comprise data transmission or data reception. In addition, the adaptive predictive mobile node may execute a communication time prediction capability and identify the most advantaged time for communication at the selected location based on future predicted node locations. For systems with advanced routing capabilities located in individual nodes such as ad hoc multi-hop networks or hybrid networks, the adaptive predictive node may also execute a route prediction capability and identify the most advantaged route for present or future communication. The adaptive predictive mobile node then communicates based on the identified criteria.
In a second mode of operation, an adaptive predictive node can schedule communication with another node through communications with the autonomous or distributed network control entity. The addition of scheduling to the efficient power control and routing provides an additional level of reliability for communicating nodes. In this mode, the adaptive predictive node identifies optimal characteristics for communication as described above in the first mode of operation (e.g., location, power level, transmission parameters, communication time, and route.) Instead of communicating only when the criteria are met, the adaptive predictive mobile node communicates a request for scheduling based on the criteria to the network control entity. The network control entity determines whether the network can support the scheduling request and communicates the determination to the adaptive predictive node. If the request can be supported successfully, the node will communicate based on the criteria. If the request cannot be supported successfully, the node may identify alternative criteria and communicate another scheduling request to the network control entity.